More than half (56%) of UK workers believe they are monitored by their boss at work, research from the TUC claims.

The union said this could take a variety of forms, including monitoring internet use, tracking people's locations and timing toilet breaks.

It said workers feared surveillance data was being used to set unfair targets and "take away autonomy".

TUC boss Frances O'Grady said it threatened to "undermine morale".

"Monitoring toilet breaks, tracking every movement and snooping on staff outside of working hours creates fear and distrust," she said.

"New technologies should not be used to whittle away our right to privacy, even when we're at work. Employers should discuss and agree workplace monitoring policies with their workforces - not impose them upon them."

According to the research, the least acceptable forms of surveillance are:

The use of facial recognition software and mood monitoring (76% against)
The monitoring of social media accounts outside of work (69% against)
The recording of a worker's location on wearable or handheld devices (67% against)
The monitoring of keyboard strokes (57% against)

However it found 70% of staff think workplace monitoring will become more common in the future. And only 38% said they felt able to challenge forms of surveillance that they felt uncomfortable with.

In one case study provided by the TUC, HGV driver Trevor said the use of monitoring technology had become "a major cause of stress".

He said in-cab cameras allowed his employers to "constantly monitor" driver behaviour, including how often they stopped for breaks and the routes they took.

"At first it was just a tracker system to let the employer see the vehicle's location. That wasn't a problem. But the company kept on stepping up the technology."

In another example, Kirsty, security worker from Yorkshire said she had discovered colleagues were using CCTV to spy on staff at a supermarket .

The 18-year-old said she discovered colleagues had used a security camera to "zoom in" on a woman's backside.

"She spoke to her manager about what had happened," the TUC said. "But her manager wanted to avoid problems... and persuaded her not to put in a grievance."